A major limitation to using mammalian cell-based biosensors for field testing of drinking water samples is the difficulty of maintaining cell viability and sterility without an on-site cell culture facility. This paper describes a portable automated bench-top mammalian cell-based toxicity sensor that incorporates enclosed fluidic biochips containing endothelial cells monitored by Electric Cell-substrate Impedance Sensing (ECIS) technology. Long-term maintenance of cells on the biochips is made possible by using a compact, self-contained disposable media delivery system. The toxicity sensor monitors changes in impedance of cell monolayers on the biochips after the introduction of water samples. The fluidic biochip includes an ECIS electronic layer and a polycarbonate channel layer, which together reduce initial impedance disturbances seen in commercially available open well ECIS chips caused by the mechanics of pipetting while maintaining the ability of the cells to respond to toxicants. A curve discrimination program was developed that compares impedance values over time between the control and treatment channels on the fluidic biochip and determines if they are significantly different. Toxicant responses of bovine pulmonary artery endothelial cells grown on fluidic biochips are similar to cells on commercially-available open well chips, and these cells can be maintained in the toxicity sensor device for at least nine days using an automated media delivery system. Longer-term cell storage is possible; bovine lung microvessel endothelial cells survive for up to four months on the fluidic biochips and remain responsive to a model toxicant. This is the first demonstration of a portable bench top system capable of both supporting cell health over extended periods of time and obtaining impedance measurements from endothelial cell monolayers after toxicant exposure.

IntroductionThe prevalence of impaired cutaneous wound healing is high and treatment is difficult and often ineffective, leading to negative social and economic impacts for our society. Innovative treatments to improve cutaneous wound healing by promoting complete tissue regeneration are therefore urgently needed. Mesenchymal stromal cells (MSCs) have been reported to provide paracrine signals that promote wound healing, but (i) how they exert their effects on target cells is unclear and (ii) a suitable delivery system to supply these MSC-derived secreted factors in a controlled and safe way is unavailable. The present study was designed to provide answers to these questions by using the horse as a translational model. Specifically, we aimed to (i) evaluate the in vitro effects of equine MSC-derived conditioned medium (CM), containing all factors secreted by MSCs, on equine dermal fibroblasts, a cell type critical for successful wound healing, and (ii) explore the potential of microencapsulated equine MSCs to deliver CM to wounded cells in vitro.MethodsMSCs were isolated from the peripheral blood of healthy horses. Equine dermal fibroblasts from the NBL-6 (horse dermal fibroblast cell) line were wounded in vitro, and cell migration and expression levels of genes involved in wound healing were evaluated after treatment with MSC-CM or NBL-6-CM. These assays were repeated by using the CM collected from MSCs encapsulated in core-shell hydrogel microcapsules.ResultsOur salient findings were that equine MSC-derived CM stimulated the migration of equine dermal fibroblasts and increased their expression level of genes that positively contribute to wound healing. In addition, we found that equine MSCs packaged in core-shell hydrogel microcapsules had similar effects on equine dermal fibroblast migration and gene expression, indicating that microencapsulation of MSCs does not interfere with the release of bioactive factors.ConclusionsOur results demonstrate that the use of CM from MSCs might be a promising new therapy for impaired cutaneous wounds and that encapsulation may be a suitable way to effectively deliver CM to wounded cells in vivo.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-015-0037-x) contains supplementary material, which is available to authorized users.

Endothelial permeability can be altered by tumor necrosis factor-alpha (TNF-alpha), a cytokine released in association with inflammation-induced tissue injury. In the subendothelial matrix, fibronectin (Fn) influences endothelial cell adhesion by the interaction of integrins with RGD and non-RGD attachment sites in Fn. We compared the effect of TNF-alpha, RGD-containing peptides (GRGDSP), or antibody to alpha 5 beta 1-integrins on the protein permeability of bovine lung endothelial monolayers as assessed by transendothelial 125I-labeled albumin clearance. We also examined the influence of purified human plasma fibronectin (hFn) on this permeability response. TNF-alpha, RGD peptides, and antibodies to alpha 5 beta 1-integrins elicited a dose- and time-dependent increase in protein permeability as well as a reorganization and/or disruption of the endogenous Fn matrix. A control RGE peptide (GRGESP) as well as immunoglobulin G purified from nonimmune rabbit serum did not increase endothelial protein permeability or disrupt the endogenous fibrillar Fn pattern in the matrix. Likewise, a LDV peptide derived from the alternatively spliced type III connecting segment (IIICS) within bovine Fn (bFn) was unable to increase permeability of the bovine endothelial monolayer. Co-incubation of purified soluble hFn (300 or 600 micrograms/ml) with either TNF-alpha, the RGD peptide, or the antibody to alpha 5 beta 1-integrins prevented the increase in endothelial permeability. This protective effect was also observed when the purified hFn (600 micrograms/ml) was added after the TNF-alpha-induced increase in endothelial permeability had taken place. Immunofluorescent analysis confirmed the incorporation of the hFn into the subendothelial matrix and its co-localization with the endogenous bFn. The similar alteration of the subendothelial matrix after exposure to RGD peptides, anti-alpha 5 beta 1-antibodies, or TNF-alpha, coupled with the ability for hFn to attenuate the permeability increase typically elicited by all three agents, suggests that disruption of cell-matrix interactions may be the mechanism by which TNF-alpha alters endothelial permeability.

A number of toxicity sensors for testing field water using a range of eukaryotic cell types have been proposed, but it has been difficult to identify sensors with both appropriate sensitivity to toxicants and the potential for long-term viability. Assessment of bovine pulmonary artery endothelial cell (BPAEC) monolayer electrical impedance with electric cell-substrate impedance sensing (ECIS) showed promise in a previous systematic evaluation of toxicity sensor technologies. The goal of the study reported here was to improve toxicant responsiveness and field portability of this cell-based toxicity sensor. A variety of human cells, non-human mammalian cells, and non-mammalian vertebrate cells were screened for sensitivity to 12 waterborne industrial chemicals. The results of this assessment show that bovine lung microvessel endothelial cell (BLMVEC) monolayers and iguana heart (IgH-2) cell monolayers could detect nine out of the 12 waterborne industrial chemicals, an improvement over the seven chemicals previously detected using BPAEC monolayers. Both the BLMVEC and IgH-2 cell monolayers were tested for their ability for long-term survival on the ECIS test chips in a laboratory environment. Both cell lines were able to maintain high impedance readings on the ECIS electrodes for 37 days, a key trait in developing a field-portable toxicity sensor for water. Cell line optimization has greatly contributed to the on-going development of a field-portable cell-based biosensor that detects with sensitivity a wide range of waterborne toxicants.